The belief that men and women are very different and this should be strongly reflected in society, language, and the law.

The belief that men and women are slightly different, besides superficial biological differences.

Most dictionaries regard the first two beliefs as sexist, but the third belief as generally not sexist. Some people, particularly masculists, hold that only the first belief is sexist. Others, particularly feminists, hold that all three beliefs are sexist. Sexism can also refer to simple hatred of men (misandry) or women (misogyny).

In practice, people's beliefs range along a continuum from the first position, which is the most sexist, to the third position, which is least sexist. For example, some people believe that women should have equal access to all jobs except a few religious positions. Others believe that while women are superior to men in a few aspects, in most aspects men are superior to women.

Sexist beliefs are a species of essentialism, which holds that individuals can be understood (and often judged) based on the characteristics of the group to which they belong, in this case, their sex group (male or female).

Sexism against women is often called chauvinism, though chauvinism is actually a wider term for any extreme and unreasoning partisanship on behalf of a group to which one belongs, especially when the partisanship includes malice and hatred towards a rival group.

While the view that women are superior to men is also sexism, only in recent years has an awareness of this "reverse sexism[?]" begun developing in public discourse.

Sexual discrimination is illegal in many countries. Most countries have laws that give special rights or privileges to one sex (feminists claim: mostly to men; masculists claim: mostly to women). Some countries ban sex discrimination but still have preferential laws in their law books.